The present invention relates generally to a zoom lens, and more particularly to a wide-angle yet high-magnification zoom lens system best suited for use on cameras, etc.
From relatively old times, high-magnification zoom lenses for use with cameras have been developed in TV camera and chine camera applications. On video cameras, on the other hand, innovation has been spurred for both commercial and consumer purposes since their widespread use. For a zoom lens having high magnification and a field angle of 70xc2x0 or greater on its wide-angle side, a very high level of optical design is known to be required. one commonly used old type of zoom lens system comprises, in order from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having positive refracting power, as typically shown in JP-B 2-48087. A great feature of this system is that both the first and fourth lens groups remain fixed during zooming.
There is a version stemming from this type, which is based on the concept of locating a front converter in the first lens group, as typically set forth in U.S. Pat. No. 3,682,534. This version is of large size due to an increased number of lenses, and is used in a focusing mode relying chiefly on the first lens group of the basic arrangement.
There is also proposed a wide-angle yet high-magnification zoom lens system comprising, from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having positive refracting power, wherein the second to fourth lens groups are movable during zooming and focusing is carried out with the fourth lens group, as typically set forth in JP-A 6-148520. So far, this system has been used in video applications.
For instance, JP-A 9-5628 shows a zoom lens of the type comprising, in order from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having negative refracting power and a fourth lens group having positive refracting power. This type is one predecessor of the wide-angle yet high-magnification zoom lens system according to the present invention as will be described later. In this type, too, the same focusing mode as mentioned above is used.
For instance, JP-A 7-20381 shows a zoom lens of the type comprising, in order from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having positive refracting power, wherein all the lens groups are movable during zooming.
The aforesaid zoom lens systems are found to have difficulty in accommodating to future image pick devices expected to increase in the number of pixels, although their lens arrangement is simple. In other words, these zoom lens systems have been originally developed for conventional silver salt film cameras. For instance, U.S. Pat. No. 4,299,454 shows a zoom lens system comprising, in order from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having positive refracting power which are all movable for zooming, and having a field angle of 80xc2x0 or greater at its wide-angle end.
JP-B 58-33531 has already showed a zoom lens system having a field angle of about 74xc2x0 to about 19xc2x0 and a zoom ratio of about 5 and comprising, in order from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having positive refracting power. A great feature of this system is that the first and second lens groups are moved as an integral unit for focusing.
U.S. Pat. No. 4,896,950 shows a zoom lens system encompassing a field angle range of about 74xc2x0 to about 8.3xc2x0, and comprising, in order from its object side, a first lens group having positive refracting power, a second lens group negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having positive refracting power, with the fifth lens group remaining fixed during zooming. Focusing is carried out with the second lens group having large power, as typically shown in JP-A 9-184982.
How to move the third lens group for focusing is typically disclosed in JP-A 10-133109, and the lens system disclosed therein is characterized by its large size and power profile. How to move back the fourth lens group for focusing is typically disclosed in JP-A 11-133303.
A high-magnification zoom lens system having a wide angle layout with its telephoto end including even a super-telephoto range such as one contemplated herein is susceptible to shakes during camera manipulation, which may otherwise cause a deterioration in image-formation capability. To this end, some compensation mechanism is needed. How to move an image in such a direction as to counteract an image movement on an image-formation plane due to shakes, etc. has been proposed in the prior art. For instance, JP-A 63-202714 shows a method of moving a part of image pickup lenses as a correction lens system in a direction vertical with respect to an optical axis which an optical system is assumed to have.
A primary purpose of the present invention is to develop a wide-angle yet high-magnification zoom lens system best suited for use on cameras, etc.
Some wide-angle yet high-magnification zoom lens systems have been proposed for conventional video cameras; however, never until now is any optical system having optical performance enough to fit for image pickup devices having more pixels than ever before proposed. In addition, much is still left to be desired in terms of the optical performance, and affinity for CCDs or the like, of silver salt cameras.
In view of an image pickup device having a microlens and influences of aliasing due to chromatic aberrations, etc., there is still growing demand for a zoom lens system, which is suitable for conventional video cameras and provides an optical system having a certain degree of telecentric nature. optical design based on a zoom lens for conventional video cameras makes a zoom lens system very large, and so offers a practically grave problem.
In view of such states of the prior art as explained above, one object of the present invention is to provide a zoom lens system of reduced size, which is applicable to a relatively large image pickup device and can keep sufficient image-formation capability even with a zoom ratio of about 10 or greater at a wide-angle end of 70xc2x0 or greater.
Another object of the present invention is to provide a zoom lens system of reduced size, which can be operated in a proper focusing mode.
Yet another object of the present invention is to provide a zoom lens system of reduced size, which can compensate for the movement of an image by moving lens groups in a proper manner.
According to one aspect of the present invention, these objects are achievable by the provision of a zoom lens system comprising, in order from an object of the zoom lens system, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having positive refracting power, characterized in that:
for zooming from a wide-angle end to a telephoto end of said zoom lens system, a spacing between said first lens group and said second lens group and a spacing between said third lens group and said fourth lens group become wide and a spacing between said second lens group and said third lens group and a spacing between said fourth lens group and said fifth lens group become narrow, and
the following conditions are satisfied:
2.0 less than f1/fw less than 8.0xe2x80x83xe2x80x83(1)
0.4 less than |f2/fw| less than 1.0xe2x80x83xe2x80x83(2)
0.3 less than f3/fT345 less than 1.2xe2x80x83xe2x80x83(3)
0.6 less than |f4|/fT345 less than 5.0xe2x80x83xe2x80x83(4)
0.5 less than f5/fT345 less than 4.0xe2x80x83xe2x80x83(5)
where fw is the focal length of said zoom lens system at said wide-angle end, f1 is the focal length of said first lens group, f2 is the focal length of said second lens group, f3 is the focal length of said third lens group, f4 is the focal length of said fourth lens group, f5 is the focal length of said fifth lens group, and fT345 is the focal length of said third lens group to said fifth lens group at said telephoto end.
According to another aspect of the present invention, there is provided a zoom lens system comprising, in order from an object of the zoom lens system, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having positive refracting power, characterized in that:
for zooming from a wide-angle end to a telephoto end of said zoom lens system, a spacing between said first lens group and said second lens group and a spacing between said third lens group and said fourth lens group become wide and a spacing between said second lens group and said third lens group and a spacing between said fourth lens group and said fifth lens group become narrow, and
said zoom lens system is focused on a finite object by moving said third lens group or a lens or lenses therein.
According to yet another aspect of the present invention, there is provided a zoom lens system comprising, in order from an object of the zoom lens system, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having positive refracting power, characterized in that:
for zooming from a wide-angle end to a telephoto end of said zoom lens system, a spacing between said first lens group and said second lens group and a spacing between said third lens group and said fourth lens group become wide and a spacing between said second lens group and said third lens group and a spacing between said fourth lens group and said fifth lens group become narrow, and
said zoom lens system is focused on a finite object by moving said fourth lens group or a lens or lenses therein.
According to a further aspect of the present invention, there is provided a zoom lens system comprising, in order from an object of the zoom lens system, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having positive refracting power, characterized in that:
for zooming from a wide-angle end to a telephoto end of said zoom lens system, a spacing between said first lens group and said second lens group and a spacing between said third lens group and said fourth lens group become wide and a spacing between said second lens group and said third lens group and a spacing between said fourth lens group and said fifth lens group become narrow, and
said zoom lens system is focused on a finite object by moving said fifth lens group or a lens or lenses therein.
According to a further aspect of the present invention, there is provided a zoom lens system comprising, in order from an object of the zoom lens system, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having positive refracting power, characterized in that:
for zooming from a wide-angle end to a telephoto end of said zoom lens system, each of said first lens group to said fifth lens group moves while said first lens group and said third lens group move toward said object side during said zooming in such a way that spacings between said first lens group and said second lens group and between said third lens group and said fourth lens group become wide,
a fluctuation of an image plane position with said zooming is compensated for by non-linear movement of at least said third lens group, said fourth lens group or said fifth lens group, and
the following conditions are are satisfied:
2.0 less than f1/fw less than 8.0xe2x80x83xe2x80x83(1)
0.4 less than |f2/fw| less than 1.0xe2x80x83xe2x80x83(2)
0.3 less than f3/fT345 less than 1.2xe2x80x83xe2x80x83(3)
0.6 less than |f4|/fT345 less than 5.0xe2x80x83xe2x80x83(4)
0.5 less than f5/fT345 less than 4.0xe2x80x83xe2x80x83(5)
where fw is the focal length of said zoom lens system at said wide-angle end, f1 is the focal length of said first lens group, f2 is the focal length of said second lens group, f3 is the focal length of said third lens group, f4 is the focal length of said fourth lens group, f5 is the focal length of said fifth lens group, and fT345 is the focal length of said third lens group to said fifth lens group at said telephoto end.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.